Electronic camera

ABSTRACT

A photographic lens system for forming an object image is placed in the lens barrel of an electronic camera. In a camera body, a beam splitter for forming branched optical paths and an image sensing element for photoelectrically converting the formed object image are arranged. An optical filter attached to a filter cap is inserted between the beam splitter and the image sensing element. The filter cap intimately contacts with the perimeter of the exit surface of the beam splitter and the perimeter of the image sensing surface of the image sensing element, thereby forming closed spaces, between the optical filter and the beam splitter and between the optical filter and the image sensing element, which allow incident light to pass through.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Applications No. 2000-123102, Apr. 24,2000; and 2000-132672, May 1, 2000, the entire contents of both of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to an electronic camera and, moreparticularly, to an electronic camera capable of preventingdeterioration of the picture quality and deterioration of the quality ofa finder image caused by adhesion of dust, and at the same time allowingeasy replacement/disassembly of optical members.

[0003] In an electronic camera, if dust adheres to an optical memberthrough which incident light to an image sensing element passes, aphotographed picture is influenced by the dust. When this is the case,it is highly likely that even rubbish of a very small size, i.e., dust,which is not a problem in a silver halide camera, appears as a black doton a photographed frame and deteriorates the picture quality. This ismainly because the size of the image sensing surface of an image sensingelement is smaller than that of a silver halide film used in a silverhalide camera. Adhesion of dust to optical members is particularly a bigproblem for an image sensing element having a high pixel density(multiple pixels), because such an image sensing element is required tohave a high picture quality.

[0004] In addition, the zoom magnification at the focusing plane of anoptical finder of an electronic camera is larger than that of a silverhalide camera. Therefore, even rubbish of a very small size, i.e., dust,which is of no problem in a silver halide camera is highly likely toappear as a black dot in a finder field and deteriorate the quality of afinder image.

[0005] To solve these problems, in a digital still camera disclosed inJpn. Pat. Appln. KOKAI Publication No. 11-109203, a lens and an opticalfilter are fixed in a sealed state in a cylindrical sealing member, andthis cylindrical sealing member is attached to a substrate for mountingan image sensing element so as to cover this image sensing elementtightly. That is, in this camera, a closed space is formed between thelens and the optical filter through which incident light to the imagesensing element passes, and around the image sensing element. Thisprevents deterioration of the picture quality caused by adhesion ofdust.

[0006] In this digital still camera disclosed in Jpn. Pat. Appln. KOKAIPublication No. 11-109203, however, once a unit including the componentsin the cylindrical sealing member is assembled, it is not easy todisassemble the unit in order to replace the parts in the cylindricalsealing member. That is, this conventional structure in which theoptical members in the vicinity of the image sensing element are coveredwith the sealing member to thereby prevent invasion and adhesion of duststill has antinomic problems: improving the picture quality andfacilitating replacement/disassembly of optical members.

[0007] Also, a camera containing a focal-plane shutter having front andrear curtains is known as a silver halide camera (a camera using asilver halide film). Since the film surface must be shielded exceptduring exposure in a silver halide camera, this focal-plane shutteroperates as follows.

[0008] Before exposure, the front curtain is always in a shieldingposition, and the rear curtain is in a retraction position. By a releaseoperation, the front curtain moves to a retraction position to uncoverthe film surface, and the film surface is exposed to light. After apredetermined time has elapsed, the rear curtain in the retractionposition moves to shield the film surface and complete the exposure.That is, the operation timings of the front and rear curtains determinethe shutter speed. When the shutter speed is low (e.g., 1/500 SEC ormore), the rear curtain moves after the front curtain retracts. When theshutter speed is high, the rear curtain begins to move while the frontcurtain is moving. In this case, the exposure time is determined by thewidth (size) of a slit gap between the trailing end of the front curtainand the leading end of the rear curtain (slit shutter mode).

[0009] In an electronic camera, on the other hand, a time correspondingto the exposure time in a silver halide camera can be set by an elementshutter which is defined by turn on/off of an image sensing element forphotoelectric conversion, e.g., a CCD. However, even an electroniccamera uses a mechanical shutter for the following reasons. First, aninterlace CCD requires the operation of a mechanical shutter at the endof exposure. Second, a progressive CCD must be shielded by a mechanicalshutter immediately after exposure is completed by an element shutter,in order to prevent smear (therefore, exposure is preferably terminatedby a mechanical shutter).

[0010] For example, Jpn. Pat. Appln. KOKAI Publication No. 11-122542disclosed an electronic camera containing a focal-plane shutter havingonly one of front and rear curtains. Also, Jpn. Pat. Appln. KOKAIPublication No. 11-218838 disclosed an electronic camera containing afocal-plane shutter having a large number of sectors functioning as ashutter which also serves as a stop. The latter publication alsodescribes that a focal-plane shutter having front and rear curtains isalso usable.

[0011] In an electronic camera containing the conventional focal-planeshutter, e.g., in each of the electronic cameras disclosed in the abovetwo publications, the shutter is placed closely in front of a CCD. Thisis so because the role of the focal-plane shutter is to shield the imagesensing surface of the CCD. This similarly holds for a silver halidecamera.

[0012] The focal-plane shutter operates a considerable number of timesat high speed. Therefore, wear caused by contact of the sectors produceswear dust. In a silver halide camera, deterioration of the picturequality caused by this wear dust is hardly a problem because the size ofa silver halide film is large. However, as described previously, if weardust adheres to the cover glass of a CCD in an electronic camera, thisadhered wear dust appears as a black dot in a photographed frame anddeteriorates the picture quality. The reasons are, for example, that theimage sensing surface of a CCD is much smaller than a silver halidefilm, and the cover glass is very close to the image sensing surface.

BRIEF SUMMARY OF THE INVENTION

[0013] The present invention has been made in consideration of theseproblems of the prior art, and has as its object to provide anelectronic camera capable of preventing deterioration of the picturequality caused by adhesion of dust to optical members through whichincident light to an image sensing element passes, and at the same timeallowing easy replacement/disassembly of these optical members.

[0014] It is another object of the present invention to provide anelectronic camera capable of preventing deterioration of the quality ofa finder image or the like caused by adhesion of dust to optical membersthrough which incident light to an optical finder unit or the likepasses, and at the same time allowing easy replacement/disassembly ofthese optical members.

[0015] It is still another object of the present invention to preventdeterioration of the picture quality caused by wear dust produced by afocal-plane shutter, in an electronic camera containing the focal-planeshutter.

[0016] According to a first aspect of the present invention, there isprovided an electronic camera comprising

[0017] a photographic lens configure to form an object image,

[0018] an image sensing element configured to photoelectrically convertthe formed object image,

[0019] a light guiding device configured to guide incident light from anobject, which is incident from the photographic lens, to a first opticalpath to the image sensing element and a second optical path differentfrom the first optical path,

[0020] an optical filter disposed between the light guiding device andthe image sensing element, and

[0021] a filter holding member made of an elastic material to hold theoptical filter, the filter holding member comprising a first portionthat surrounds and holds an outer-diameter portion of the opticalfilter, and a second portion that forms a closed space between theoptical filter and the light guiding device, and the second portionbeing connected to the first portion and intimately contacting with thatsurface of the light guiding device, which faces the optical filter, soas to surround the first optical path.

[0022] According to a second aspect of the present invention, there isprovided an electronic camera comprising

[0023] a photographic lens configure to form an object image,

[0024] an image sensing element configured to photoelectrically convertthe formed object image,

[0025] a light guiding device configured to guide incident light from anobject, which is incident from the photographic lens, to a first opticalpath to the image sensing element and a second optical path differentfrom the first optical path,

[0026] an optical member disposed on the second optical path in thevicinity of the light guiding device, and

[0027] an elastic member configured to form a closed space between theoptical member and the light guiding device, the elastic memberintimately contacting with opposite surfaces of the optical member andthe light guiding device and surrounding a space between the oppositesurfaces so as to surround the second optical path.

[0028] According to a third aspect of the present invention, there isprovided an electronic camera comprising

[0029] a photographic lens configure to form an object image,

[0030] an image sensing element configured to photoelectrically convertthe formed object image,

[0031] an optical filter disposed between the photographic lens and theimage sensing element,

[0032] a focal-plane shutter disposed between the photographic lens andthe optical filter to mechanically interrupt incident light to the imagesensing element, and

[0033] a holding frame configured to surround the image sensing elementand the optical filter and to form a closed space between the imagesensing element and the optical filter.

[0034] According to a fourth aspect of the present invention, there isprovided an electronic camera comprising

[0035] a photographic lens configure to form an object image,

[0036] an image sensing element configured to photoelectrically convertthe formed object image,

[0037] an optical filter disposed between the photographic lens and theimage sensing element,

[0038] a light guiding device disposed between the photographic lens andthe optical filter to guide incident light from an object, which isincident from the photographic lens, to a first optical path to theimage sensing element and a second optical path different from the firstoptical path,

[0039] a focal-plane shutter disposed between the photographic lens andthe light guiding device to mechanically interrupt incident light to theimage sensing element, and

[0040] a holding frame configured to surround the image sensing elementand the optical filter and to form a closed space between the imagesensing element and the optical filter.

[0041] Additional objects and advantages of the invention will be setforth in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention may be realized and obtained bymeans of the instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0042] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate presently preferredembodiments of the invention and, together with the general descriptiongiven above and the detailed description of the preferred embodimentsgiven below, serve to explain the principles of the invention.

[0043]FIG. 1 is a perspective view showing the external appearance of anelectronic camera according to an embodiment of the present invention;

[0044]FIG. 2 is a sectional view showing the internal structure of theelectronic camera shown in FIG. 1;

[0045]FIG. 3 is an enlarged sectional view showing the main parts of thestructure shown in FIG. 2;

[0046]FIGS. 4A and 4B are perspective views showing the assembled stateand disassembled state, respectively, of a casing used in a camera bodyof the electronic camera shown in FIG. 1;

[0047]FIG. 5 is a perspective view showing the disassembled state of aholding frame structure used in the electronic camera shown in FIG. 1;

[0048]FIG. 6 is a perspective view showing the relationship between afront plate of the holding frame structure, a lens barrel, and a frontcover of the casing in the electronic camera shown in FIG. 1;

[0049]FIG. 7 is a sectional view showing the internal structure of anelectronic camera according to another embodiment of the presentinvention;

[0050]FIG. 8 is a block diagram showing the whole configuration,particularly, circuits in the electronic camera shown in FIG. 7;

[0051]FIG. 9 is a timing chart showing the operation sequence of ashutter at a low shutter speed in the electronic camera shown in FIG. 7;

[0052]FIG. 10 is a timing chart showing the operation timing of theshutter at a high shutter speed in the electronic camera shown in FIG.7;

[0053]FIGS. 11A and 11B are views showing the relationship between frontand rear curtains and the image sensing surface of an image sensingelement in a setup state and a ready state, respectively, common to lowand high shutter speeds in the electronic camera shown in FIG. 7;

[0054]FIGS. 12A and 12B are views showing the relationship between thefront and rear curtains and the image sensing surface of the imagesensing element when the shutter speed is high in the electronic camerashown in FIG. 7;

[0055]FIG. 13 is a view for explaining the relationship between theaperture diameter of a stop and the exposure time;

[0056]FIG. 14 is a view showing the state in which optical parts shownin FIG. 7 are arranged in accordance with the structure of aconventional electronic camera:

[0057]FIG. 15 is a view showing the arrangement of the optical parts ofthe electronic camera shown in FIG. 7;

[0058]FIG. 16 is a view showing the arrangement of optical parts of anelectronic camera according to still another embodiment of the presentinvention; and

[0059]FIG. 17 is a view showing the arrangement of electronic parts ofan electronic camera according to still another embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

[0060] Embodiments of the present invention will be described below withreference to the accompanying drawings. In the following explanation,the same reference numerals denote components having substantially thesame functions and configurations, and a duplicate explanation will bemade only where necessary.

[0061]FIG. 1 is a perspective view showing the outer appearance of anelectronic camera according to an embodiment of the present invention.FIG. 2 is a sectional view showing the internal structure of theelectronic camera. FIG. 3 is an enlarged sectional view showing the mainparts of the electronic camera. As shown in FIG. 1, this electroniccamera 10 includes a camera body 12, and a lens barrel 14 detachablyattached to the front surface of a casing 13 of the body 12. FIG. 1 alsoshows a two-step release switch 15 for starting photographing, and arelease terminal 16 and a strobe terminal 17 for connecting lines forremotely controlling release and strobe operations.

[0062] In the lens barrel 14, zoom lenses 21 a and 21 b, a stop 22, anda focusing lens 23 are arranged in this order from the incident lightside. The zoom lenses 21 a and 21 b and the focusing lens 23 construct aphotographic lens system for forming an object image (in FIG. 2, thearrangement of these lenses is schematically shown).

[0063] At the entrance of the camera body 12, a beam splitter 24 (lightguiding device or light splitting device) for splitting an incidentoptical image from the photographic lens system toward a CCD imagesensing element 30 and an optical finder unit 40 is placed. This beamsplitter 24 is formed by combining two prisms, i.e., lower and upperprisms 25 and 26. The CCD image sensing element (photoelectricconversion element) 30 photoelectrically converts the incident objectimage formed on the image sensing surface, and outputs it as anelectrical signal.

[0064] Two optical filters 28 and 29 are inserted between the beamsplitter 24 and the image sensing element 30. The filter 28 is an IR cutfilter for cutting infrared radiation, which is formed by deposition ona glass surface. The filter 29 is a low-pass filter for preventingmoire, which is formed by stacking two or more quartz plates. Thesefilters 28 and 29 are integrated by adhesion.

[0065] The beam splitter 24, the optical filters 28 and 29, and theimage sensing element 30 are installed in a form to be described laterin the camera body 12 by a holding frame structure 32. A first printedcircuit board 33 is placed at the back of this holding frame structure32, and the image sensing element 30 is connected to this first printedcircuit board 33. In addition, a second printed circuit board 34 isplaced below the holding frame structure 32 so as to form a right angleto the first printed circuit board 33.

[0066] An optical finder unit 40 is attached to the holding framestructure 32 in accordance with the optical path branched upward by thebeam splitter 24. This optical finder unit 40 includes a finder frame 41bent at a right angle. A focusing plate 42 for focusing and a fieldframe plate 43 are attached to that side of the finder frame 41, whichfaces the beam splitter 24. In this finder frame 41, a plurality oflenses 44 and 45 and a mirror 46 are arranged (the lens arrangement isschematically shown in FIG. 2). The light beam split toward the opticalfinder unit 40 by the beam splitter 24 is guided to a finder window atthe back of the camera body 12 via these optical members.

[0067] An image display LCD 18 is placed in the middle of the backsurface of the camera body 12. This image display LCD 18 is used as aphotographic finder in recording mode and as a monitor for reproducing arecorded photographed picture in playback mode.

[0068]FIG. 4A is a perspective view showing the assembled state of thecasing 13 of the camera body 12. FIG. 4B is a perspective view showingthe disassembled state of the casing 13. As shown in FIGS. 4A and 4B,this casing 13 is composed of a front cover 51, a rear cover 52, and anupper cover 53, all of which are metal products having a high thermalconductivity, e.g., aluminum diecast products. These covers 51, 52, and53 are joined by using known screw members (not shown). The covers 51,52, and 53 are thermally connected as their contact surfaces intimatelycontact with each other, thereby constructing an integratedheat-radiating casing having large thermal capacity, i.e., the casing13, for radiating heat to the outside of the camera.

[0069]FIG. 5 is a perspective view showing the disassembled state of theholding frame structure 32. As shown in FIGS. 3 and 5, this holdingframe structure 32 includes a prism frame (heat-transfer frame member)61, a bottom plate 62, and a rear plate 63, all of which are metalproducts having a high thermal conductivity, e.g., aluminum diecastproducts. The holding frame structure 32 also includes filter caps 66and 67 and a sealing member 68 assembled inside the prism frame 61. Allof the filter caps 66 and 67 and the sealing member 68 are products madefrom highly elastic materials, e.g., synthetic rubber molded products.

[0070] The prism frame 61 is so constructed as to insert the beamsplitter 24 from the lower opening of this prism frame 61. The bottomplate 62 is fastened to the prism frame 61 by using known screw members(not shown) so as to close this lower opening. The prism frame 61 andthe bottom plate 62 are thermally connected as their contact surfacesintimately contact with each other, thereby constructing an integratedheat-transfer frame member having large thermal capacity.

[0071] On the bottom surface 62, a leaf spring 65 for pressing the beamsplitter 24 in a biased state at a predetermined position is disposed.The lower prism 25 is positioned by the biasing force of this leafspring 65. In this state, those contact surfaces 25 a and 25 b at theupper and lower edges of the reference oblique surface of the lowerprism 25, which protrude from the upper prism 26, contact withcorresponding stop surfaces 61 a and 61 b, respectively, formed on theprism frame 61. The upper prism 26 is positioned as it is pushed againstthe reference oblique surface of the lower prism 25 by the sealingmember 68.

[0072] The rear plate 63 is much larger than the image sensing element30 and intimately contacts with the rear surface of the image sensingelement 30. This rear plate 63 is fastened to the prism frame 61 byusing known screw members (not shown) so as to close the rear opening ofthe prism frame 61. The rear plate 63 is thermally connected to theprism frame 61 as their contact surfaces intimately contact with eachother, thereby forming a thick heat-transfer path from the rear plate 63to the prism frame 61. A pair of slits 63 a are formed in this rearplate 63. A lead frame 35 for electrically connecting the image sensingelement 30 and the printed circuit board 33 is disposed through theseslits 63 a.

[0073] As shown in FIGS. 3 and 6, the holding frame structure 32 furtherincludes a front plate 71 placed on the front side of the prism frame61. This front plate 71 is a metal product having a high mechanicalstrength and a high thermal conductivity, e.g., a steel plate product.FIG. 6 is a perspective view showing the relationship between the frontplate 71 of the holding frame structure 32, the lens barrel 14, and thefront cover 51 of the casing 13.

[0074] The prism frame 61 is fastened to the front plate 71 by usingknown screw members (not shown). This prism frame 61 is thermallyconnected to the front plate 71 as their contact surfaces intimatelycontact with each other, thereby forming a thick heat-transfer path fromthe prism frame 61 to the front plate 71. Furthermore, the front plate71 is fastened to the front cover 51 of the casing 13 by using knownscrew members (some screw members are shown in FIG. 6). This front plate71 is thermally connected to the front cover 51 as their contactsurfaces intimately contact with each other, thereby forming a thickheat-transfer path from the front plate 71 to the front cover 51.

[0075] Also, a portion of the lens barrel 14 constructs a heat-radiatingbarrel 72 for radiating heat to the outside of the camera. Thisheat-radiating barrel 72 is made of a thermally conductive material,e.g., aluminum. The rest of the lens barrel 14 is formed with asynthetic resin. The heat-radiating barrel 72 is fastened to the frontplate 71 by using known screw members (not shown). This lens barrel 72is thermally connected to the front plate 71 as their contact surfacesintimately contact with each other, thereby forming a thickheat-transfer path from the front plate 71 to the heat-radiating barrel72.

[0076] As described above, a thick heat-transfer path is formed from theimage sensing element 30 to the casing 13 of the camera body 12 and tothe heat-radiating barrel 72 of the lens barrel 14, both having largethermal capacity, via the holding frame structure 32 which includes,e.g., the prism frame 61 having large thermal capacity. Since the heatgenerated by the image sensing element 30 is rapidly released to theoutside of the camera through this heat-transfer path, it is possible toprevent a rise of the temperature of the image sensing element 30 andthereby prevent deterioration of the picture quality. In particular, thelens barrel 14 has a large exposure area to the outside and hence has ahigh heat-radiating effect. Note that the members such as the prismframe 61 of the holding frame structure 32 forming the heat-transferpath and the casing 13 and the heat-radiating barrel 72 for radiatingheat to the outside of the camera are all originally necessary members.Therefore, the internal structure of the apparatus can be flexibly madecompact without adding any extra members.

[0077] Referring back to FIG. 5, the filter caps 66 and 67 assembledinside the prism frame 61 are separately molded products and fastened tothe front and rear sides, respectively, of the integrated filters 28 and29. These filter caps 66 and 67 are inserted, as they hold the filters28 and 29, into the prism frame 61 from its rear opening, before therear plate 63 is attached to the prism frame 61. The filter cap 66 ispositioned by abutting it against the exit surface of the beam splitter24. The filter cap 67 is positioned by abutting it against an internalstop surface 61 c of the prism frame 61.

[0078] As shown in FIG. 3, the filter cap 66 has as its main portion asurrounding portion 66 a for holding the filter 28 by surrounding it. Inaddition, this filter cap 66 has an extended portion 66 b whichintimately contacts with the perimeter of the exit surface of the beamsplitter 24 by elastic deformation, thereby forming, between the filter28 and the beam splitter 24, a substantially closed space through whichincident light to the image sensing element 30 passes. Similarly, thefilter cap 67 has as its main portion a surrounding portion 67 a forholding the filter 29 by surrounding it. This filter cap 67 also has anextended portion 67 b which intimately contacts with the perimeter ofthe image sensing surface of the image sensing element 30 by elasticdeformation, thereby forming, between the filter 29 and the imagesensing element 30, a substantially closed space through which incidentlight to the image sensing element 30 passes.

[0079] The beam splitter 24, the filters 28 and 29, and the imagesensing element 30 are assembled against the elasticity of the filtercaps 66 and 67. Consequently, the surrounding portions 66 a and 67 aintimately contact with the beam splitter 24 and the image sensingelement 30, respectively.

[0080] Since the filter caps 66 and 67 surround the whole perimeters ofthe filters 28 and 29, it is possible to reliably prevent damage to theedges of these filters 28 and 29 and thereby prevent the generation ofparticles. Also, since the filter caps 66 and 67 form a substantiallyclosed space surrounding the optical path between the beam splitter 24and the image sensing element 30, deterioration of the picture qualitycaused by invasion and adhesion of dust can be prevented. Furthermore,the filter caps 66 and 67 and the sealing member 68 intimately contactonly with the beam splitter 24 and the image sensing element 30. Thisfacilitates disassembling the beam splitter 24, the filters 28 and 29,and the image sensing element 30, when any of these components is to bereplaced. Although the filter caps 66 and 67 are separate members inthis embodiment, they can also be an integrated member.

[0081] The sealing member 68 is attached to the upper opening of theprism frame 61 which opens to the optical finder unit 40. This sealingmember 68 has a flange portion 68 a in its upper portion. The sealingmember 68 is positioned by clamping this flange portion 68 a in anintimate contact state between the prism frame 61 and the finder frame41. The sealing member 68 also has a cylindrical portion 68 b whichintimately contacts with the perimeter of the exit surface of the beamsplitter 24 by elastic deformation, thereby forming, between thefocusing plate 42 and the beam splitter 24, a substantially closed spacethrough which incident light to the optical finder unit 40 passes.

[0082] The beam splitter 24 and the finder frame 41 are assembledagainst the elasticity of the sealing member 68. Consequently, thesealing member 68 intimately contacts with the beam splitter 24 and thefinder frame 41.

[0083] That is, a substantially closed space is also formed for theoptical finder unit 40, in the vicinity of the focusing plate 42, by thesealing member 68. Therefore, deterioration of the quality of a finderimage caused by invasion and adhesion of dust can be prevented.Additionally, since the sealing member 68 intimately contacts only withthe beam splitter 24, disassembly of the parts around this beam splitter24 is not interfered with.

[0084] In the above embodiment, aluminum is used as the material of thefront cover 51, the rear cover 52, and the upper cover 53 of the casing13 and the prism frame (heat-transfer frame member) 61, the bottom plate62, and the rear plate 63 of the holding frame structure 32, from theviewpoint of thermal conductivity and light weight. However, similareffects can be obtained even when zinc or magnesium is used as thematerial of these parts.

[0085]FIG. 7 is a sectional view showing the internal structure of anelectronic camera according to another embodiment of the presentinvention. As shown in FIG. 7, this electronic camera 110 includes acamera body 112, and a lens barrel 114 detachably attached to the frontsurface of a casing 113 of the body 112.

[0086] In the lens barrel 114, two zoom lenses 121, a stop 122, and afocusing lens 123 are arranged along an optical path L1 in this orderfrom the incident light side. The two zoom lenses 121 and the focusinglens 123 construct a photographic lens system for forming an objectimage.

[0087] At the entrance of the camera body 112, a beam splitter 124(light guiding device or light splitting device) for splitting anincident object image from the photographic lens system toward a CCDimage sensing element 130 (an optical path L2) and an optical finderunit 150 (an optical path L3) is placed. Between this beam splitter 124and the image sensing element 130, a shutter 125 and two types ofoptical filters 128 and 129 are arranged along the optical path L2.

[0088] The shutter 125 is a focal-plane shutter having a front curtain126 and a rear curtain 127 to be opened and closed in a way to bedescribed later. The filter 128 is an IR cut filter for cutting infraredradiation. The filter 129 is a low-pass filter for preventing thegeneration of moire. The CCD image sensing element (photoelectricconversion element) 130 photoelectrically converts an incident objectimage formed on an image sensing surface 130 a and outputs it as anelectrical signal.

[0089] The beam splitter 124 and the shutter 125 are held in a firstholding frame 142. This holding frame 142 is mounted on and fixed to amounting frame 141 which is fastened to the casing 113 of the body 112.The filters 128 and 129 are held in a second holding frame 143. Thissecond holding frame 143 forms a substantially closed space forpreventing invasion of dust and the like, between the filter 129 and theimage sensing element 130. The second holding frame 143 is mounted onand fixed to the first holding frame 142.

[0090] A first printed circuit board 144 is disposed at the end portionof the second holding frame 143. The image sensing element 130 ismounted on this first printed circuit board 144. In addition, a secondprinted circuit board 145 is disposed below the holding frames 142 and143 so as to form a right angle to the first printed circuit board 144.

[0091] The optical finder unit 150 is mounted on the first holding frame143 along the optical path L3 branched from the optical path L2 by thebeam splitter 124. This optical finder unit 150 has a lens 152 and aneyepiece 154 placed at the two ends of a finder frame 151 bent at aright angle, and a mirror 153 placed in the bent portion of the finderframe 151. A light beam separated by the beam splitter 124 is guided toa finder window 155 at the back of the camera body 112 via these opticalmembers 152, 153, and 154.

[0092] An image display LCD 115 is placed in the middle of the backsurface of the camera body 112. This image display LCD 115 is used as aphotographic finder in recording mode and as a monitor for reproducing arecorded photographed picture in playback mode.

[0093] As described earlier, the focal-plane shutter 125 operates aconsiderable number of times at high speed, so wear by contact of thesectors (the front curtain 126 and the rear curtain 127) produces weardust. In the electronic camera 110 according to this embodiment,therefore, the shutter 125 is placed away from the image sensing element130 and closer to the incident light side than the filters 128 and 129.In addition, the second holding frame 143 forms a substantially closedspace for preventing invasion of dust and the like, between the filter129 and the image sensing element 130. Hence, adhesion of wear dust tothe cover glass of the image sensing element 130 can be prevented.Accordingly, it is possible to avoid phenomenon in which adhered weardust appears as a black dot on the frame to deteriorate the picturequality.

[0094]FIG. 8 is a block diagram showing the overall configuration,particularly, circuits in the electronic camera 110.

[0095] An optical image of an object to be photographed is input via thephotographic lens systems 121 and 123 and formed on the CCD imagesensing element 130. During this image formation, in accordance with theset conditions and the photographing environment, the zoom lenses 121,the stop 122, and the focusing lens 123 are driven by a zoom motor 132,a stop actuator 133, and an AF (Automatic Focusing) motor 134,respectively, under the control of a driving controller 131. Also, thefront curtain 126 and the rear curtain 127 of the shutter 125 are drivenby a front curtain actuator 136 and a rear curtain actuator 137,respectively, under the control of a driving controller 135. Each ofthese actuators 133, 136, and 137 is a combination of a motor andsolenoid.

[0096] The image sensing element 130 photoelectrically converts theincident object image formed on the image sensing surface 130 a, andoutputs it as an electrical signal. The signal from the image sensingelement 130 is input to an A/D (analog/digital) converter 164 via animage sensing circuit 163 for signal processing. The signal from the A/Dconverter 164 is input to a system controller 161 via an AE (AutomaticExposure)/AF (Automatic Focusing) circuit 165, and to an internal memory166 via a bus 162.

[0097] The internal memory 166 is connected to the system controller 161via the bus 162. The image data stored in this internal memory 166 iscompressed and recorded in a memory card 168 in a card slot via the bus162 and an I/F (interface) 169. That is, the input image data isconverted into a signal recordable in the memory card 168, under thecontrol of the system controller 161.

[0098] The image display LCD 115 is connected to the bus 162 via a VRAM(Video RAM) 171 and a driving controller 172. The image data suppliedfrom the image sensing element 130 or the memory card 168 and stored inthe internal memory 166 is transferred to the image display LCD 115 viathe driving controller 172, and displayed as an image.

[0099] An operation unit 173 is also connected to the system controller161. This operation unit 173 includes various operation buttons andoperation keys. An operation command is input to the system controller161 via the operation unit 173 to set the operation of this electroniccamera.

[0100] Furthermore, a strobe emission unit 174 including, e.g., astrobe, strobe controller, and strobe capacitor is connected to thesystem controller 161.

[0101] The operation of the shutter 125 performed in photographing modeof the electronic camera 110 under the control of the shutter drivingcontroller 135 and the system controller 161 will be described in detailbelow. FIGS. 9 and 110 are timing charts showing the operation sequencesof the shutter 125 at a low shutter speed (e.g., 1/500 msec or more) anda high shutter speed (e.g., less than 1/500 msec), respectively. FIGS.11A and 11B are views showing the relationship between the front curtain126, the rear curtain 127, and the image sensing surface 130 a of theimage sensing element 130 in a setup state and ready state common to thelow and high shutter speeds. FIGS. 12A and 12B are views showing therelationship between the front curtain 126, the rear curtain 127, andthe image sensing surface 130 a of the image sensing element 130 at thehigh shutter speed.

[0102] The upper ends of the front curtain 126 and the rear curtain 127are taken up by rolls which are driven by the motors of the actuators136 and 137, respectively. The lower ends of these front and rearcurtains 126 and 127 are taken up by rolls which are driven by springs.The front and rear curtains 126 and 127 are charged when taken up by therollers on the motor side. When the solenoids of the actuators 136 and137 are turned off, the front and rear curtains 126 and 127 are releasedand taken up by the rolls on the spring side at high speed.

[0103] In the charged state, the front curtain 126 is closed to shieldthe image sensing surface 130 a of the image sensing element 130, andthe rear curtain 127 is opened to uncover the image sensing surface 130a. In the released state, the front curtain 126 is opened to uncover theimage sensing surface 130 a of the image sensing element 130, and therear curtain 127 is closed to shield the image sensing surface 130 a.That is, the opening/closure of the front curtain 126 is exactlyopposite to that of the rear curtain 127 in each of the charged andreleased states.

[0104]FIG. 11A shows the setup state initially set in photographingmode. In this state, both the front and rear curtains 126 and 127 areopened to uncover the image sensing surface 130 a (the front curtain 126is released, and the rear curtain 127 is charged). In this state, theimage sensing element 130 is used to monitor the object on the imagedisplay LCD 115 or perform photometry for AE (Automatic Exposure)/AF(Automatic Focusing). FIG. 11B shows the ready state immediately beforea release SW (switch) is turned on. In this state, the front curtain 126is closed to shield the image sensing surface 130 a, and the rearcurtain 127 is opened to uncover the image sensing surface 130 a (boththe front and rear curtains 126 and 127 are charged).

[0105] As shown in FIG. 9, when the release SW is turned on from theready state shown in FIG. 11B at the low shutter speed, the frontcurtain 126 is first released to uncover the image sensing surface 130a. In substantially synchronism with this, an element shutter (definedby turn on/off of the image sensing element 130) is turned on to startimage sensing. When a predetermined certain image sensing time haselapsed, the rear curtain 127 is released to shield the image sensingsurface 130 a. After that, the signal from the image sensing element 130is transferred and read out. That is, a time (to be referred to as anexposure time hereinafter) corresponding to the exposure time of asilver halide camera is determined by the period from the ON of theelement shutter to the shielding by the mechanical shutter 125.

[0106] On the other hand, as shown in FIG. 10, when the shutter speed ishigh, the element shutter is already ON in the ready state shown in FIG.11B. When the release SW is turned on from this ready state, the frontcurtain 126 is first released, and the rear curtain 127 is then releasedto start moving while the front curtain 126 is moving. In other words,the front and rear curtains 126 and 127 are released with a certain timelag between them and expose the image sensing surface 130 a to lightwhile running parallel to each other (FIG. 12A). When the rear curtain127 shields the image sensing surface 130 a (FIG. 12B), the exposure iscomplete. After that, the signal from the image sensing element 130 istransferred and read out. That is, a time (to be referred to as anexposure time hereinafter) corresponding to the exposure time of asilver halide camera is determined by the width (size) of a slit gap 125a between the trailing end of the front curtain 126 and the leading endof the rear curtain 127 (slit shutter mode).

[0107] In the electronic camera according to this embodiment, theshutter 125 is positioned away from the image sensing surface 130 a ofthe image sensing element 130, compared to the conventional electroniccamera. For example, the arrangement of the optical parts of theelectronic camera 110 of this embodiment is as shown in FIG. 15.However, when these optical parts are arranged in accordance with thestructure of the conventional electronic camera, the arrangement is asshown in FIG. 14. Hence, the camera is influenced by the aperture area(aperture diameter) of the stop 122 more strongly than in theconventional structure. That is, in slit shutter mode when the shutterspeed is high, the exposure time of the image sensing surface largelychanges in accordance with the aperture diameter of the stop 122 for thesame shutter speed. This will be explained below.

[0108]FIG. 13 is a view for explaining the relationship between theaperture diameter of the stop and the exposure time. Referring to FIG.13, a position P1 closely in front of the image sensing surface 130 a ofthe image sensing element 130 indicates the position of the shutter 125in the conventional structure shown in FIG. 14. A position P2 away fromthe image sensing surface 130 a indicates the position of the shutter125 in this embodiment shown in FIG. 15.

[0109] In slit shutter mode when the shutter speed is high, an exposuretime T of the image sensing surface 130 a is calculated by

T=(S+d)/v  (1)

[0110] where S is the width of the slit 125 a, v is the shutter speed(the running speeds of the front and rear curtains 126 and 127, and thespeeds of the two curtains are equal), and d is the diameter of a lightbeam at the shutter 125 (the position P1 or P2).

[0111] The diameter d of the light beam is calculated by

d=(f−x)D/f  (2)

[0112] where f is the focal length of the zoom lens 121 (the distancefrom the zoom lens 121 to the image sensing surface 130 a), x is thedistance from the zoom lens 121 to the shutter 125 (the position P1 orP2), and D is the aperture diameter of the stop 122.

[0113] When the shutter 125 is in the position P1 closely in front ofthe image sensing surface 130 a as in the conventional structure shownin FIG. 14, the distance x has a value close to the focal length f inequation (2), so the diameter d of the light beam at the shutter 125 hasa very small value regardless of the value of the aperture diameter D ofthe stop 122. When this is the case, the diameter d of the light beam ismuch smaller than the width S of the slit 125 a. Accordingly, the widthS of the slit 125 a and the shutter speed v are dominant as elements fordetermining the exposure time T. That is, this exposure time T is notlargely influenced by the aperture diameter D of the stop 122.

[0114] By contrast, when the shutter 125 is in the position P2 away fromthe image sensing surface 130 a as in the structure of this embodimentshown in FIG. 15, the value of the distance x is smaller than that ofthe focal length f, so the diameter d of the light beam at the shutter125 has a relatively large value. In this case, the diameter d of thelight beam has a value not small when compared to the width S of theslit 125 a in equation (1). In addition, the diameter d of the lightbeam greatly changes in accordance with a change in the aperturediameter D of the stop 122. This increases the influence of the diameterd of the light beam as an element for determining the exposure time T.That is, the exposure time T is largely influenced by the aperturediameter D of the stop 122.

[0115] For example, the right-hand side of FIG. 13 exaggerativelyindicates the relationship between diameters d2 and d4 of the light beamat the position P2 and the width S of the slit 125 a when the aperturediameter of the stop 122 is set to F2 and F4. As shown in FIG. 13, ifthe diameters d2 and d4 of the light beam are about four and two times,respectively, the width S of the slit 125 a, exposure times T2 and T4 ofthe image sensing surface 130 a when the aperture diameter of the stop122 is set to F2 and F4 have a ratio of 5:3 from equation (1), i.e.,they are largely different from each other, even for the same shutterspeed v.

[0116] To solve this problem, in the electronic camera 110 according tothis embodiment, the shutter driving controller 135 controls driving ofthe front and rear curtains 126 and 127 in accordance with the set valueof the aperture area of the stop 122 formed by the system controller 161and with the set value of the shutter speed of the shutter 125, suchthat the exposure time of the image sensing surface 130 a is equal to apredetermined exposure time to be obtained by the set value of theshutter speed. That is, even when the set value of the shutter speedremains the same, the shutter driving controller 135 operates the frontand rear curtains 126 and 127 in different modes in accordance with theset value of the aperture area of the stop 122, thereby obtaining apredetermined exposure time. As described above, this can eliminate theproblem posed when the shutter 125 is placed in the position away fromthe image sensing surface 130 a of the image sensing element 130compared to the conventional electronic camera.

[0117]FIGS. 16 and 17 are views showing the arrangements of opticalparts of electronic cameras according to still other embodiments of thepresent invention.

[0118] In the embodiment shown in FIG. 16, a shutter 125 is placedcloser to the incident light side than a beam splitter 124. In theembodiment shown in FIG. 17, a click return mirror (optical pathswitching device) 180 is disposed, instead of a beam splitter 124, as alight guiding device for forming a branched optical path to an opticalfinder. The beam splitter 124 can be moved between a position Pr atwhich the direction of a light beam passing through a photographic lenssystem is changed toward the optical finder and a position Ps at whichthis light beam is passed toward an image sensing element 130.

[0119] In the embodiments shown in FIGS. 16 and 17, the shutter 125 issimilarly disposed away from the image sensing element 130 and closer tothe incident light side than filters 128 and 129. Therefore, it ispossible to prevent adhesion of wear dust from the focal-plane shutter125 to the image sensing surface of the image sensing element 130, andthereby avoid deterioration of the picture quality. In theseembodiments, as in the embodiment shown in FIG. 7, it is desirable toform a substantially closed space for preventing invasion of dust andthe like, between the image sensing element 130 and the optical member(in this case, the filter 129) closely in front of the image sensingelement 130, by using an appropriate holding frame.

[0120] In each of the above embodiments, the focal-plane shutter 125 isthe shutter 125 having the front and rear curtains 126 and 127. However,the present invention is also applicable to a focal-plane shutter havingonly one curtain (sector) or a large number of sectors.

[0121] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details and representativeembodiments shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. An electronic camera comprising: a photographiclens configure to form an object image; an image sensing elementconfigured to photoelectrically convert the formed object image; a lightguiding device configured to guide incident light from an object, whichis incident from the photographic lens, to a first optical path to theimage sensing element and a second optical path different from the firstoptical path; an optical filter disposed between the light guidingdevice and the image sensing element; and a filter holding member madeof an elastic material to hold the optical filter, the filter holdingmember comprising a first portion that surrounds and holds anouter-diameter portion of the optical filter, and a second portion thatforms a closed space between the optical filter and the light guidingdevice, and the second portion being connected to the first portion andintimately contacting with that surface of the light guiding device,which faces the optical filter, so as to surround the first opticalpath.
 2. The camera according to claim 1, wherein the optical filter andthe light guiding device are assembled against an elasticity of thefilter holding member, thereby allowing the second portion of the filterholding member to intimately contact with the light guiding device. 3.The camera according to claim 1, wherein the filter holding memberfurther comprises a third portion that forms a closed space between theoptical filter and the image sensing element, the third portion beingconnected to the first portion and intimately contacting with thatsurface of the light guiding device, which faces the optical filter, soas to surround the first optical path.
 4. The camera according to claim3, wherein the filter holding member comprises first and second memberssplit in the longitudinal direction of the optical axis, the second andthird portions are arranged in the first and second members,respectively, and the first and second members intimately contact witheach other.
 5. The camera according to claim 1, wherein the lightguiding device comprises a light splitting device configured to splitthe incident light to the first and second optical paths.
 6. The cameraaccording to claim 5, wherein the light splitting device comprises abeam splitter.
 7. The camera according to claim 1, further comprising:an optical member disposed on the second optical path in the vicinity ofthe light guiding device; and an elastic member configured to form aclosed space between the optical member and the light guiding device,the elastic member intimately contacting with opposite surfaces of theoptical member and the light guiding device and surrounding a spacebetween the opposite surfaces so as to surround the second optical path.8. An electronic camera comprising: a photographic lens configure toform an object image; an image sensing element configured tophotoelectrically convert the formed object image; a light guidingdevice configured to guide incident light from an object, which isincident from the photographic lens, to a first optical path to theimage sensing element and a second optical path different from the firstoptical path; an optical member disposed on the second optical path inthe vicinity of the light guiding device; and an elastic memberconfigured to form a closed space between the optical member and thelight guiding device, the elastic member intimately contacting withopposite surfaces of the optical member and the light guiding device andsurrounding a space between the opposite surfaces so as to surround thesecond optical path.
 9. The camera according to claim 8, wherein theoptical member and the light guiding device are assembled against anelasticity of the elastic member, thereby allowing the elastic member tointimately contact with the optical member and the light guiding device.10. The camera according to claim 8, wherein the second optical pathcomprises an optical path to an optical finder unit configured to forman image for visual check of an object image.
 11. An electronic cameracomprising: a photographic lens configure to form an object image; animage sensing element configured to photoelectrically convert the formedobject image; an optical filter disposed between the photographic lensand the image sensing element; a focal-plane shutter disposed betweenthe photographic lens and the optical filter to mechanically interruptincident light to the image sensing element; and a holding frameconfigured to surround the image sensing element and the optical filterand to form a closed space between the image sensing element and theoptical filter.
 12. The camera according to claim 11, further comprisinga light guiding device disposed between the photographic lens and theoptical filter to guide incident light from an object, which is incidentfrom the photographic lens, to a first optical path to the image sensingelement and a second optical path different from the first optical path.13. The camera according to claim 12, wherein the light guiding devicecomprises a light splitting device configured to split the incidentlight to the first and second optical paths.
 14. The camera according toclaim 13, wherein the light splitting device comprises a beam splitter.15. The camera according to claim 12, wherein the light guiding devicecomprises an optical path switching device configured to switch firstand second states in which the incident light is output to the first andsecond optical paths, respectively.
 16. The camera according to claim15, wherein the optical path switching device comprises a movablemirror.
 17. The camera according to claim 11, further comprising: a stopdevice configured to limit the amount of light beam incident on theimage sensing element; a stop controller configured to form a set valueof the aperture area of the stop device; a shutter controller configuredto form a set value of the shutter speed of the focal-plane shutter; andan exposure controller configured to operate the focal-plane shutter indifferent modes in accordance with the set value of the aperture area ofthe stop, even when the set value of the shutter speed remains the same,thereby obtaining a predetermined exposure time.
 18. An electroniccamera comprising: a photographic lens configure to form an objectimage; an image sensing element configured to photoelectrically convertthe formed object image; an optical filter disposed between thephotographic lens and the image sensing element; a light guiding devicedisposed between the photographic lens and the optical filter to guideincident light from an object, which is incident from the photographiclens, to a first optical path to the image sensing element and a secondoptical path different from the first optical path; a focal-planeshutter disposed between the photographic lens and the light guidingdevice to mechanically interrupt incident light to the image sensingelement; and a holding frame configured to surround the image sensingelement and the optical filter and to form a closed space between theimage sensing element and the optical filter.
 19. The camera accordingto claim 18, further comprising: a stop device configured to limit theamount of light beam incident on the image sensing element; a stopcontroller configured to form a set value of the aperture area of thestop device; a shutter controller configured to form a set value of theshutter speed of the focal-plane shutter; and an exposure controllerconfigured to operate the focal-plane shutter in different modes inaccordance with the set value of the aperture area of the stop, evenwhen the set value of the shutter speed remains the same, therebyobtaining a predetermined exposure time.
 20. The camera according toclaim 18, wherein the light guiding device comprises a light splittingdevice configured to split the incident light to the first and secondoptical paths.
 21. The camera according to claim 18, wherein the lightguiding device comprises an optical path switching device configured toswitch first and second states in which the incident light is output tothe first and second optical paths, respectively.